The invention relates to a microcomputer controlled apparatus which employs batteries as power supplies for word processors and personal computers, and which includes a battery voltage detection circuit for detecting a drop in the power supply voltage.
Recently, microcomputer controlled apparatuses of the hand held type such as word processors and personal computers have appeared on the market. Many of these microcomputer controlled apparatuses use batteries as their power supply. In conventional microcomputer controlled apparatuses, which use batteries, there are provided battery voltage detection circuits and indicators which inform operators about the consumption of the batteries. Further, in a conventional battery voltage detection circuit, the battery voltage is detected, and if the battery voltage drops below a specific reference value, microprocessors controlling peripheral equipments, such as printers and floppy disc drives, are stopped and indicators are turned on. The operators see the indicators, confirm the consumption of the batteries, and then turn off power supply switches and exchange the batteries with new ones.
In conventional microprocessor controlled apparatuses provided with battery voltage detection circuits, however, when the battery voltage drops below a fixed reference value, the microprocessor may be stopped. In that case, after the peripheral equipments stop operating, if the switches are left on for a while the load current of the battery may decrease owing to the stop operation of the peripheral equipments and the voltage may rise. The battery voltage detection circuits erroneously detect this as a normal voltage and reset the microprocessor. Then the microprocessor begins to execute operations again. As a result, the peripheral equipments begin to operate again, which causes an increase in power consumption and a drop in the battery voltage. The microprocessor may then be stopped again. If this is caused repeatedly, the battery voltage will drop so excessively as to be below the fixed reference value which guarantees the operation of the microprocessor. This may cause further trouble resulting in misoperation of the microcomputer causing erroneous program execution.
Therefore, to prevent this trouble, besides the battery voltage detection circuit for detecting whether the battery voltage is higher or not than the first reference voltage necessary for the normal operation of the microprocessor, the conventional apparatus has a second battery voltage detection circuit, provided with a second reference voltage being higher than the first reference voltage, for detecting whether a battery voltage is higher or not than the second reference voltage. The second battery voltage detection circuit informs the operator about consumption of the battery in the case where the battery voltage drops below the second reference voltage.
At that time, since the battery voltage doesn't drop below the first reference voltage, it doesn't stop the operation of the peripheral equipments and allows the operators to use the apparatus. In such cases, the batteries can be exchanged early enough that the microprocessors can be prevented from misoperating. But just after the battery voltage becomes below the second reference value, if the battery is exchanged with a new one, it may be uneconomical to throw away the old battery.